This invention pertains to the art of protective devices and more particularly to a thread protecting device.
The invention is particularly applicable to use with conventional pipe or tube fittings and machine parts having pipe threads thereon and will be described with particular reference thereto; however, it will be appreciated to those skilled in the art that the invention could be readily adapted for use in other environments, for example, where similar protective devices are employed to protect other types of fragile or destructible threaded areas.
Conventional pipe threads and pipe fitting threads are, of course, generally V-shaped in cross section. Because of the handling techniques generally employed with such items, the threads are often "bounced" around or otherwise mistreated during manufacture, shipment and use. Such mistreatment can cause particular damage to the crests of the threads by way of nicks, indentations and deformation resulting in their being unusable. Various forms and types of thread protecting devices have heretofore been suggested and employed in the industry, all with varying degrees of success. It has been found that the defects present in most prior thread protecting devices are such that the devices themselves are of limited economic value.
Typically, these prior thread protectors have variously comprised cup-shaped members formed from relatively heavy rubber, plastic, paper or the like. Generally, the internal diameters of at least a portion of these protectors have been slightly smaller than the outer diameter of the pipe or fitting threads. This dimensional arrangement facilitated resiliently gripping of the threads so that the protecting devices could not be easily dislodged during shipping and handling. Oftentimes, beads, thread forms and the like were formed inside the protective devices to enhance the overall gripping power.
Problems inherent in such prior art protectors included, among others, unacceptable results due to tolerance variations in both the threads and the protectors. For example, the protectors generally had to be constructed so that they could properly be held in place with the widest set of tolerance variations possible, i.e., maximum thread undersize dimension and maximum protector oversize dimension. Consequently, when the opposite tolerance variation situation was present, i.e., maximum thread oversize and maximum protector undersize, the protectors were extremely difficult to properly place over the threads and often, extremely difficult to remove when so desired. The difficulty thus encountered resulted in an increase in the overall unit cost and customer dissatisfaction. Further, unless the protectors were made from highly resilient material, undesired splitting of the protectors was a frequent occurrence. This "resiliency" requirement should not be confused with "elasticity" inasmuch as a protector must have some rigidity to function adequately by allowing the open end thereof to be telescoped over the threads without some preliminary expansion step being involved.
Other problems have also been present in prior protectors where it was desired to make the protectors tight fitting enough to prevent accidental removal. In prior plastic constructions, the cup-shaped plastic protectors become locked on the threads due to plastic deformation of the protectors which was then followed by a setting of the plastic in that deformed shape. That is, prior, conventional plastic shell arrangements tended to tightly circumferentially grip the thread crest so that over a period of time, the relatively thick walls took a permanent set by virtue of a small amount of plastic flow which formed crests and valleys within the cup interior. When it was subsequently desired to remove the protectors from the threads by applying an axial force thereagainst, it was found that removal could not always be effected by hand. It was essentially required, therefore, to unthread the protectors from the protecting condition which, also, oftentimes required a substantial amount of force and effort. In these instances a customer has been faced with incurring a small additional labor cost due to the extra time required in such unthreading type removals and, at times, it has been necessary to cut the protectors away from the threads which resulted in even more time being consumed.
Although the relative time involved in the difficult removal situations is not considered to be particularly substantial when taken on a piecemeal basis, it will be appreciated that when protectors of these prior types are disposed on, for example, tube fittings which are then to be attached to equipment moving along an assembly line at a constant set speed, the need for uniform motions to strip the protectors and affix the fittings are extremely important to an overall smooth and efficient production operation. Variations in the removal process are both time consuming and irritating to workers. The time consuming aspect adds undesirable costs which are ultimately either absorbed by the manufacturer which reduces his profits or passed along to the consumer which places the manufacturer in a less competitive position.
Still another problem with the prior protectors was that they had to be made with relatively heavy walls. This result was due to the method by which they were made, i.e., injection molding, and the necessity for having substantial resiliency. This need only added further cost to these prior protectors.